Wobbler Syndrome in Thoroughbreds: Racing Prognosis Examined

Near the end of his long and storied life, one of the greatest Thoroughbred racehorses of all times, 1978 Triple Crown winner Seattle Slew, was diagnosed with cervical vertebral malformation (CVM, commonly known as wobbler syndrome). He underwent two surgeries to correct the problem and continued his job as a breeding stallion until he died in 2002.

Today, many young Thoroughbreds are diagnosed with CVM. Some undergo surgery before their racing careers, some are euthanized before the problem becomes too severe, and others are treated with a more conservative approach. Crystal Hoffman, DVM, with Peterson & Smith Equine Hospital in Ocala, Fla., reviewed a study on conservative CVM treatment at the 2011 American College of Veterinary Internal Medicine Forum, held June 15-18 in Denver, Colo., that indicated in some cases, Thoroughbreds diagnosed and treated using this method early in the course of the disease can recover to have a successful racing career.

Horses affected by CVM essentially have a damaged spinal cord. The major causes of spinal cord damage include malformation of the cervical (neck) vertebrae, trauma to the vertebrae, or excessive growth of surrounding soft tissue. Affected horses typically have a history of ataxia (incoordination) or weakness with no other visible abnormalities. Veterinarians usually diagnose a horse with CVM after a thorough clinical examination along with myelograms (a procedure in which dye is injected into the spinal canal and a set of radiographs is taken) that confirm bony abnormalities and narrow cervical spinal spaces in the horse's neck. Hoffman cited several previous studies that showed poor return to racing for CVM-affected horses.

The conservative approach to treating the disease (which was the focus of the current study) involved medical treatment with NSAIDs, vitamin E, exercise restriction, and a diet change to slow young horse's growth rate. Conservative treatment is most commonly used in young horses that have not yet finished maturing; the theory behind this approach is that a decrease in growth rate can allow for remodeling of the vertebrae to increase the size of the canal. Following that up with corticosteroids, rest, and turnout in a small paddock has been observed to help the young horse proceed normally with his life.

More invasive surgical interventions involve inserting a metal apparatus called a Bagby basket designed to fuse the horse's vertebrae, which can widen the cervical spaces to reduce the amount of pressure on the spinal cord. This procedure can be performed on older horses that have matured as well as on youngsters and has reported success rates as high as 75%.

Hoffman discussed a recent retrospective study that examined 119 Thoroughbreds diagnosed with CVM from 2002-2010 and evaluated their racing careers post-conservative treatment. Sixty five percent of the affected horses were treated conservatively, while the remaining 35% were euthanized prior to treatment.

Hoffman reported that horses with a neurologic grade of 2 or lower (on a scale of 1 to 5) fared better than the group with more lesions graded at 2.5 or higher. Horses with spinal degenerative arthritis, narrowing of the vertebral canal (stenosis), or kyphosis (spinal curvature)--all diagnosed via radiograph--were less likely to return to racing. Horses with less extensive bony lesions as seen on radiographs had better outcomes.

Of the treated horses, Hoffman stated that only 27% were able to begin racing after receiving only conservative treatment. Hoffman added that of the 72% that did not race, some might have had success in other careers, but no follow-up information was available. Additionally, it's unclear if any opted for surgical intervention after the completion of conservative treatment.

The study results indicated that conservative treatment for young horses diagnosed with CVM can be effective in allowing horses to lead a productive life in mild cases, but more advanced cases could require surgical intervention or euthanasia. Horse owners are encouraged to discuss all treatment options with their veterinarian before opting for euthanasia.

About the Author

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado,
and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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